@function __parse-int($string, $radix: null, $guard: null) {
  @if ($guard and __is-iteratee-call($string, $radix, $guard)) {
    $radix: 10;
  }

  @if __is-falsey($string) {
    @return 0;
  }

  $string: to-upper-case(__trim($string));

  @if __is-falsey($radix) {
    $radix: if(__starts-with($string, ("0X", "#")), 16, 10);
  }

  $result: 0;
  $multiplier: if(__starts-with($string, "-"), -1, 1);
  $prefix: if(
    __starts-with($string, ("-", "+", "#")),
    1,
    if(__starts-with($string, ("0X")), 2, 0)
  );
  $char-min: __get-char-code(0);
  $char-max: $char-min + 9;
  $char-alpha-min: __get-char-code("A"); // 10
  $char-alpha-max: __get-char-code("Z");
  $char-codes: __map($string, "__get-char-code");
  $index: $prefix + 1;
  $break: false;

  @while $index <= length($char-codes) and not $break {
    $char-code: nth($char-codes, $index);

    @if $char-code >= $char-min and $char-code <= $char-max {
      $result: ($radix * $result) + ($char-code - $char-min);
    } @else if $char-code >= $char-alpha-min and $char-code < $char-alpha-max {
      $result: ($radix * $result) + ($char-code - $char-alpha-min + 10);
    } @else {
      $break: true;
    }

    $index: $index + 1;
  }

  @return $multiplier * $result;
}

/// Parses a string argument and returns an integer of the specified radix
/// (the base in mathematical numerical systems).
///
/// Similar to native JavaScript [parseInt() function](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/parseInt).
///
/// @access public
/// @group Number
/// @param {String} $string The value to parse. If string is not a string,
///  then it is converted to one. Leading whitespace in the string is ignored.
/// @param {Number} $radix An integer between 2 and 36 that represents the radix
///  (the base in mathematical numeral systems) of the above mentioned string.
/// @returns {Number} Returns the string converted to an integer, or `null`.
/// @example scss
///
/// $foo: _parse-int('10');
/// // => 10
///
/// $foo: _parse-int('#000020');
/// // => 32
///
/// $foo: _parse-int('    123');
/// // => 123

@function _parse-int($args...) {
  @return call(get-function("__parse-int"), $args...);
}